Panes of the above described type are known and are used for various purposes. From DE-OS 19 51 616, a glass pane of this type is known, wherein the pattern preferably consists of an opaque or semitransparent baking finish having a light transmittance of 0 to 40%. The fragments constituting the grating pattern, which may be square, rectangular, circular or elliptical, are said to have a length of 0.1 to about 20 mm, and the spacing or gap between the small fragments is to be 0.1 to 10 mm. The fragments may be in contact with one another, resulting in a hole grating. The glass panes having patterns of this type are intended for use as antidazzle panes or as heat protective panes, and are used, for example, also in automobiles.
From DE-AS 23 61 669, a dazzle-reducing window of the initially named type is also known, preferably for automobiles. In this known window, on the surface of the glass pane provided with the pattern, a frame-like solid strip of the opaque material is provided along its edge, by which the edges of the window frame are to be concealed from view. For the case where the glass panes are glued to the window frame, the solid frame-like edge strip serves also as a protection against ultraviolet radiation, which otherwise would lead to embrittlement of the adhesive.
In DE 27 13 892 C2, a glass pane with a pattern in the form of dots on one of its faces is described, the dots being applied in such a distribution that the sum of the surface regions of the opaque dots covers 10 to 30% of the glass surface, the size of the dots being so chosen that from 12 to 20 dots per centimeter lie in each direction. A pane of this type is intended to be used predominantly in a sports hall or games hall as a viewing wall.
EP 0 120 781 describes a glass pane of the initially named type, particularly suitable for a glass roof of an automobile. For this intended application, the pattern of opaque baking finish is to be sufficiently dense for the light transmission and accordingly the total energy transmission to be less than 30% and preferably less than 15%.
The known patterns consist of grating-like or screen-like structures, in which the individual fragments of the coating which impedes or attenuates the passage of radiation and the radiation-transmitting holes each have a constant size and are uniformly and homogeneously distributed over the entire pattern and over the entire glass surface. In specific cases, in which the light transmission is to vary from a high value to a low value, or vice versa, within the grating-like structures, grating structures are used, in which the individual fragments of the layer, or radiation-transmitting holes as the case may be in the layer, become smaller or larger by steps in one direction, whereas in the direction transversely to this they each have a constant size. Such structures are employed, especially, in dazzle-reducing filter bands in the upper region of windscreens and in the transition region between the opaque decorative frame and the fully transparent viewing area of automobile glass panes.
It has been found that the human eye is especially sensitive to uniform structures of this type and that, if the grating structure is viewed critically, as for example occurs in the production inspection of the glass panes, even very small defects are evident. If, for example, therefore a single small fragment of the grating is missing on a glass pane printed with such a uniform grating, or if only one single hole of the hole grating is closed, this leads as a rule to this defect being evident on inspection and the glass pane consequently having to be rejected.
Irregularities in the printed grating become all the more readily visible to the human eye, the higher the degree of cover of the glass pane is. In specific cases, the printed glass panes must have a very low transmission of less than about 30%, namely for example in the case where such glass panes are used as automobile roof windows. In this case, the panes are printed as a rule with an opaque, black baking finish. In other cases, for example for use in ambulance vehicles, the requirement exists that the lateral panes shall be made non-transparent when viewed from the outside by printing with an opaque, white paint, but shall permit sufficient vision in the opposite direction. If this effect is to be achieved with a surface-covering print, a high reflection is obtained on the outer face of the glass pane, by which any slight deformations or surface irregularities of the pane are emphasized. If, instead, the printing is carried out with a uniform grating print, then once again the aforementioned difficulty arises that very small defects in the grating print are easily recognizable by the eye in reflection or in transmission.